The invention relates to well servicing fluids and, more particularly, to a surfactant blend which is useful in removing oil-based mud cakes and in protecting cement slurries from oil contamination.
During the well drilling process, drilling fluids are used to create a mud cake upon the well walls of the formation being drilled through, so as to control fluid loss. The drilling fluid also serves to help in the removal of cuttings or rubble from the well through circulation to the top of the hole, and maintains stability of the hole, in addition to fluid loss control as mentioned above.
The mud cake which is left upon the walls of the hole can present a problem, however, during subsequent cementing of the well. The mud cake can affect the adherence of cement upon the well walls, particularly if the mud cake is wetted with oil, or formed from an oil-based drilling fluid.
Drilling can be carried out using a water-based fluid. Under these circumstances, removal of the mud cake is relatively easy, and subsequent slurry contamination is not a major issue. However, under certain circumstances drilling is preferred to be carried out using an oil-based drilling fluid. Under these circumstances, cementing problems can increase.
The presence of a mud cake which is wettable with oil, or formed from an oil-based drilling fluid, can completely prevent adherence of cement to the walls of the well due to incompatibility existing between the cement and organic contamination. This can lead to bad cementation and expensive cement repair, particularly if the oil-based fluid contamination occurs near a zone of interest such as an oil producing formation or the like.
One way to remove such a mud cake involves the use of organic solvents, particularly aromatic solvents, which react with the oil-wettable mud cake and dissolve same. Unfortunately, the substitution of gasoil for friendly oils to the environment, the use of additives which can change the wettability in the mud solids, and therefore on the well walls, and the formation of a highly efficient mud cake through drilling fluid additives such as polymers make organic aromatic compound-based chemical washing fluids problematic. This can lead to the use of high volumes of such chemical washes, and/or the need for spacers between treatments in order to obtain sufficient removal of the mud cake.
In addition, the use of oil-based chemical wash components can further require use of a water-based fluid as a spacer between the chemical wash and the subsequent cement slurry so as to avoid contaminating the slurry with organic phase from the wash. This, of course, also leads to increased cementation costs.
Based upon the foregoing, it is clear that the use of oil-based drilling fluid can lead to substantially higher cost compared to other types of drilling fluid due to increased need for chemical wash and spacer materials, and further due to operating time spent to obtain an adequate cement slurry formation. Of course, if problems occur during the first cementing operation, costs can be multiplied due to subsequent attempts at cementating the well.
Based upon the foregoing, it is clear that the need exists for an improved approach toward solving problems caused by mud cake formed from oil-based drilling fluid, and for solving other problems caused by same.
It is therefore, the primary object of the present invention to provide a well servicing fluid in the form of a surfactant blend which readily resolves the aforesaid issues.
It is a further object of the present invention to provide a method for treating a well having oil-based drilling fluid mud cake disposed thereon.
It is a still further object of the present invention to provide a method for cementing a well wherein the cement slurry is protected from contamination.
It is another object of the present invention to provide a method for forming a surfactant blend.
Other objects and advantages of the present invention will appear hereinbelow.